1. Technical Field
This invention relates to lances such as used for introducing an inert gas into molten metal for stirring the same or for injecting a stream of oxygen into molten metal for refining the same.
2. Description of the Prior Art
Lances for introducing gases into molten metal for various purposes are disclosed in U.S. Pat. Nos. 3,379,428 and 3,082,997, which disclose immersion lances formed of straight metal tubes forming a plurality of gas conduits arranged to direct gas downwardly into the molten metal in which the lance is positioned.
U.S. Pat. Nos. 3,645,520 and 3,898,078 disclose lances in which the gas conveying conduits are formed in several patterns, the U.S. Pat. No. 3,645,520 providing an axial metal conduit around which several tubes are spirally wound and encased in an exterior housing which may be a protective refractory. Alternate forms of the disclosure position the metal tubes in varied patterns and surrounds them with a refractory body and one such form adds an exterior housing, partly metal and partly refractory. U.S. Pat. No. 3,898,078 forms the lance of a pair of tubular members, one positioned within the other, with the inner tubular member having a relatively thick end portion in which helical passageways are formed so that gas introduced into an area between the tubular members will flow through the helical passageways which communicate with the delivery end of the lance. The lower portion of this end of the lance is covered with a suitable refractory.
U.S. Pat. Nos. 4,389,245 and 4,550,898 disclose lances having straight gas conveying conduits therein and refractory housings of cylindrical cross section thereabout and U.S. Pat. No. 4,588,170 discloses a lance which is primarily an elongated refractory body having a tubular gas conduit extending longitudinally thereof and terminating inwardly of the ends thereof in a cavity opening outwardly.
The present invention relates to a substantially improved lance for treating molten metals in which the principal body of the lance is formed of refractory material with a bore in which a metal tube is positioned and in which metal tube a plurality of smaller metal tubes in a spirally wound pattern through some of their lengths are positioned so as to engage the inner surface of the larger metal tube. A refractory core formed therein mechanically locks the smaller tubes in desired position whereby their open ends at the delivery end of the lance provide a tangential flow of gas causing a circular stirring motion in the molten metal. The novel construction of the elongated refractory body and its relatively small bore axially thereof in which the smaller metal tubes are positioned and held by the refractory core enables the lance to be effectively used in introducing gas into molten metal and contributes to its substantially longer life than has heretofore been possible with the prior art lances.